In the known way, acoustic attenuation devices for turbocharged motor vehicle engine intake lines comprise a tract through which pressurized air laden with oil is intended to travel and the air inlet and outlet ends of which are incorporated into this intake line. There are essentially two distinct types of device such as this, these including:                those with a radially external tubular casing to the end portions of which a radially internal tract structure is secured to form two annular resonance chambers with two respective widenings of the casing, for example like that described in document DE-A1-199 56 172, and        those with Helmholtz resonators which are arranged radially on the outside of an air circulation tract being separated from one another by partitions that are transverse and/or longitudinal with respect to the tract and which communicate therewith through openings formed in its wall, as illustrated in document EP-B-1 352 172 for example.        
One major disadvantage of the known attenuation devices of the type having annular resonance chambers lies in their relatively large size and in the low number of resonance chambers formed, which is generally limited to two, thus penalizing the acoustic performance for a given length of device.
As for known attenuation devices of the Helmholtz resonator type, these have the notable disadvantage of providing, over a greater or shorter length of time, an acoustic attenuation that is unsatisfactory both in respect of the hissing noises generated by the turbocharged engine (manifesting themselves in the form of pressure pulses in the low frequencies typically ranging from 1300 to 2000 Hz approximately) and in terms of the whistling noises also generated by this engine (high frequencies above around 2500 Hz).
These Helmholtz resonator devices also sometimes have the disadvantage of requiring several plastic components to be welded together, for example of requiring a cover to be welded to the wall of the resonance chamber(s), to the detriment of the method of manufacture of the device in terms of cleanliness, ease of implementation and cost, and also being potentially detrimental to the ability of the device to withstand pressure and the acoustic performance of the device, particularly on account of difficulties with controlling the geometric tolerances and/or the deformations of the welded plastic under the effect of temperature, this potentially giving rise to air leaks.